It is known to separate alkenes (e.g. propene) from alkanes (e.g. propane) by distillation. The propene-propane mixture is fed into a C.sub.3 -splitter, which typically is a 2-column distillation system. The second column is substantially equal in size to the first column. The first column separates a substantial portion of the propane to produce a chemical or refinery grade propene of at least 90 volume percent purity, typically about 96 volume percent. The second column improves the purity level to 99+ volume percent to obtain polymer grade propene. The separation of propene from propane by distillation is both difficult and costly because the process requires two large columns and is very energy intensive.
It is also known to separate alkenes from alkanes by adsorption. U.S. Pat. No. 4,917,711 describes the adsorption of an alkene from a mixture containing the alkene and an alkane using an adsorbent comprising a copper compound and a high surface area support such as silica gel or zeolite molecular sieves, such as 4A zeolite, 5A zeolite, type X zeolite or type Y zeolite.
East German Patent No. 150885 describes the separation of alkenes from alkanes using 4A zeolite which has some of its exchangeable cations replaced by calcium or magnesium ions.
U.S. Pat. No. 5,365,011 describes the separation of alkenes having 2 to 6 carbon atoms from alkanes having 2 to 6 carbon atoms by pressure swing adsorption at temperatures in the range of about 50 to about 200.degree. C. using 4A zeolite. The 4A zeolite may have up to 25% of its exchangeable sodium ions replaced by other ions, including potassium ions, calcium ions, strontium ions, etc., provided that the presence of the other ions does not cause the 4A character of the adsorbent to change.
Breck et al, "The Properties of a New Synthetic Zeolite, Type A", Journal of the American Chemical Society, Vol. 78, Number 23, 1956, pp. 5963-5977, describes the adsorption of various hydrocarbons using partially potassium-exchanged type 4A zeolite.
Because of the importance of adsorption as a method of separating alkenes from alkanes, adsorbents having enhanced alkene--alkane separation ability are continuously sought. This invention provides new adsorbents which can efficiently and effectively separate selected alkenes, particularly ethene from selected alkanes, particularly ethane.